Not able to get into recovery mode

Yes, the NX should flash over the micro-B USB if you have the SD card inserted. This is the TX2 forum, so that gets a bit confusing…TX2 has only an eMMC model. Assuming an NX with SD card model, then this should work for flash on command line (you can later run SDK Manager to add optional packages):
sudo ./flash.sh jetson-xavier-nx-devkit mmcblk0p1

If you are not using a dev kit (meaning a model with eMMC), then the previous command line would probably be wrong and flashing eMMC would end up being something like this:
sudo ./flash.sh jetson-xavier-nx-devkit-emmc mmcblk0p1

JetPack/SDKM should have downloaded and installed the “Linux_for_Tegra/” driver package content already, and also the “Linux_for_Tegra/rootfs/” content. If not, then you’d need to download and set up the driver package and sample rootfs manually.

I recommend trying with command line since there is less to go wrong.